Method for production of single-use foundry molds and apparatus for realization thereof

ABSTRACT

A molding chamber (7) accommodating pattern plates (24, 25) is supplied by a steam of air with sand mixture delivered in a direction parallel to the pattern plates (24, 25). After a time delay relative to the start of the sand delivery operation, and sand mixture is preliminarily compacted by delivering a stream of compressed air directly into the molding chamber in a direction parallel to the pattern plates, the delivery of compressed air being continued within a period of time equal to 5 to 30 percent of the duration of the sand mixture delivery operation. As a result of the delivery of compressed air, the delivery of the sand mixture is retarded and even interrupted. The stream of compressed air diverts the sand mixture in the molding chamber towards the pattern plates, thus providing a better filling of narrow deep hollows on pattern surfaces and preliminary compaction of the sand mixture. The sand delivery operation is completed after the end of the preliminary compaction. The sand mixture is finally compacted by mechanical pressing.

FIELD OF THE INVENTION

The invention relates to foundry practice and, more particularly, to amethod for the production of single-use foundry molds, and an apparatusfor realization thereof.

PRIOR ART

Known in the prior art is a method for the production of single-usefoundry molds (US, A 4313486), comprising the delivery of the sandmixture by the stream of air into the molding chamber accommodating apattern plate, in the direction parallel to the pattern plate.Concurrently with its delivery, said mixture is preliminarily compactedby the stream of compressed air in the direction perpendicular to thepattern plate. The molding chamber being filled, the mixture iscompacted by pressing.

This method is realized in the known apparatus (U.S. Pat. No.4,313,486), comprising a molding chamber formed by plates arranged inpairs, viz., upper and bottom plates, side plates, pattern plate andpressing plate, a compressed air source and a means for its deliveryinto the molding chamber. The pattern and pressing plates have cavitiesand channels for the passage of air through said cavities. The upperplate has a channel for the delivery of sand mixture into the moldingchamber, said mixture being delivered by the air stream in the directionparallel to the pattern plate. Concurrently, the compressed air isdelivered by the molding chamber air supply unit from the compressed airsource into the pressing plate cavity wherefrom it flows throughpressing plate channels into the molding chamber.

Due to a pressure differential, the air is removed into the atmospherefrom the molding chamber through channels of the pattern, upper andbottom plates. As a result, the air streams created in the moldingchamber flow both in the vertical and horizontal directions. Thehorizontal streams entrain the particles of sand mixture and carry themtowards the pattern plate, filling the deep hollows in the patterns.

However, said horizontal streams of air directed towards the patternplate, perpendicularly thereto, are created by only a part of compressedair delivered through the channels of the pressing plate, the pressureof this compressed air being equal to, or somewhat lower than, thepressure of the air which forces the sand mixture into the moldingchamber so that the power of the horizontal air streams is insufficientfor efficient filling of narrow and deep hollows in the patterns withsand mixture and for compacting said mixture therein.

Owing to the action of the created air streams on the sand mixture, thedensity of said mixture is distributed irregularly throughout the volumeof the molding chamber: the mixture layers adjoining the pattern platehave a maximum density while near the pressing plate the mixture has aminimum density and this leads to creation of voids in the foundry moldopposite the air channels in the pressing plate because the compressedair jets discharged from the channels interfere with the filling ofthese mold zones with sand mixture.

Subsequent pressing of the sand mixture by moving the pressing platetowards the pattern plate compacts the sand mixture in the layersadjoining the pressing plate; however, complete elimination of irregulardistribution of mixture density throughout the volume of the mold andvoids in the compressed air supply zones proves impossible.

Besides, the produced mold is difficult to extract from the moldingchamber without breaking the thin protruding parts of the mold, formedby narrow and deep hollows in the pattern since the pattern plate isfixed immovably and cannot move the mold out of the molding chamber.

Thus, the known method for the production of foundry molds and theapparatus for realization thereof fail to ensure making high-qualitymolds of a complex configuration.

There is another method for the production of single-use foundry molds(SU, A, 1060299), consisting in that the molding chamber incorporating apattern plate is filled with sand mixture delivered by the air stream inthe direction parallel to the pattern plate. Then, on expiration of timeequal to 8-60% of the duration of sand mixture supply, said mixture ispreliminarily compacted by the delivery of compressed air in thedirection perpendicular to the pattern plate. Final compaction of thesand mixture is performed by pressing.

The apparatus for the realization of this method comprises platesarranged in pairs and forming a molding chamber, a source of compressedair and a means for its periodical communication with the moldingchamber. Four side plates arranged in pairs opposite each other areinstalled immovably and two more plates, the upper and bottom ones,installed movably opposite to each other with a provision forreciprocating motion have, each, a cavity and channels for the passageof air through said cavity. One of the side plates has a slot for thedelivery of sand mixture into the molding chamber. The pattern platelocated inside the molding chamber is installed rigidly on the bottommovable plate and has air channels arranged coaxially with the channelsof said plate. The upper plate is installed above the slot for thedelivery of sand mixture with a provision for moving inside the moldingchamber and is provided with a means for putting the plate cavity inperiodic communication with the source of compressed air.

The air stream delivers the sand mixture through the slot in thedirection parallel to the pattern plate. On expiration of a time periodequal to 8-60% of the duration of sand mixture delivery, compressed airis delivered from its source through the means for its periodicalcommunication with the molding chamber into the upper plate cavity undera pressure which is higher than the air pressure for the delivery ofsand mixture into the molding chamber, wherefrom it flows through thechannels in the upper plate into the molding chamber in the directionperpendicular to the pattern plate.

Inasmuch as the molding chamber communicates with the atmosphere throughthe channels in the pattern plate and the compressed air enters themolding chamber through the channels in the upper part of the chamber,the pressure differential in the molding chamber together with the eddycurrents forms the air streams directed towards the pattern plate,perpendicularly thereto.

Within the above-mentioned period of time, the molding chamber is filledwith a certain amount of sand mixture which will fill the moldingchamber partly from the side of the pattern plate so that the narrowdeep hollows of the pattern will be partly filled with loose sandmixture. The air streams directed perpendicularly to the pattern platewill entrain particles of the sand mixture entering the molding chamberand carry them towards the pattern plate. Filtering through the layersof loose sand mixture that has entered the molding chamber before thestart of delivery of compressed air, the air streams will compact thesand mixture but its density will be distributed irregularly: themaximum density will be in the mixture layers adjoining the patternplate while the mixture layers fartbest from the pattern plate will havea minimum density.

Thus, the process of filling the molding chamber with the sand mixtureand compacting the latter takes place until the upper layers of the sandmixture cover the slot for the delivery of mixture into the moldingchamber. The air jets discharged from the channels interfere with thefilling of the neighboring zones of the mold with the sand mixture sothat voids are formed near said plate. The molding chamber having beenfilled with the sand mixture, the upper plate is moved towards thepattern plate, thus compacting the sand mixture by pressing. Pressingcompacts the mixture near the upper plate and raises somewhat theuniformity of mixture distribution throughout the mold volume but failsto eliminate voids in its zone opposite the compressed air deliverychannels near the pressing plate. After pressing, the bottom plate withthe pattern plate secured thereto is brought down, thus extracting thepattern from the foundry mold.

The known method and apparatus for realization thereof fail to producehigh-quality foundry molds of a complex configuration.

Besides, during extraction of patterns from the mold, the high and thinparts of said mold are often broken due to their insufficient strengthwhich is caused by insufficient density of these parts of the mold.

SUMMARY OF THE INVENTION

The main object of the invention is to provide a method for theproduction of single-use foundry molds and an apparatus for realizationthereof wherein uniform compaction of the sand mixture throughout themold volume and the design of the apparatus would ensure the productionof high-quality foundry molds of a complex configuration.

This object is achieved in the method for the production of single-usefoundry molds comprising delivery of sand mixture by an air stream intothe molding chamber incorporating a pattern plate in the directionparallel to the pattern plate and, on expiration of a time period equalto about 6-60% of the duration of mixture delivery, preliminarycompaction of said mixture by compressed air then its final compactionby pressing wherein, according to the invention, the air begins to bedischarged from the molding chamber before the beginning and in thecourse of sand mixture delivery in the direction perpendicular to thepattern plate and this discharge of air ends concurrently with the endof mixture delivery, the compressed air being delivered into the moldingchamber in the direction parallel to the pattern plate and this deliveryending before the end of delivery of the sand mixture.

The air shall be discharged from the molding chamber before filling itwith the sand mixture in order to create therein intensive horizontalair streams directed towards the pattern plate, perpendicularly thereto.

In the course of mixture delivery into the molding chamber saidhorizontal air streams deflect the sand mixture towards the patternplate which contributes to its better penetration into the narrow deephollows of the pattern.

The necessity for delivery of compressed air into the molding chamber inthe direction parallel to the pattern plate is caused by the fact thatthe streams of compressed air of said direction interacting with thestreams of air directed towards the pattern plate, perpendicularlythereto, ensure compaction of the sand mixture in the narrow deephollows of patterns and uniform compaction of said mixture throughoutthe volume of the mold.

It is practicable that the discharge of the air from the molding chambershould being 0.1-1 s before the beginning of mixture delivery.

This method of air discharge from the molding chamber is required inorder to create reliable motion of air streams towards the patternplate. The time period shorter than 0.1 s is insufficient for formingthe steady streams of air perpendicular to the pattern plate while theperiod exceeding 1 s before the delivery of sand mixture isuneconomical.

It is recommended that the delivery of compressed air into the moldingchamber should be continued within the time period equal to about 5-30%of the duration of sand mixture delivery.

The delivery into the molding chamber of compressed air in the directionparallel to the pattern plate improves the filling of narrow deephollows in the patterns with sand mixture and its preliminarycompaction.

However, this process goes together with the rise of air pressure in themolding chamber which retards, or even may stop, the delivery of sandmixture. Therefore, the delivery of compressed air into the moldingchamber should be stopped before the end of sand mixture delivery.

Said duration limits of compressed air delivery into the molding chamberare the optimum ones since, if the duration of air delivery is less than5% of the duration of mixture delivery, the effect of said air isinsufficient while the duration exceeding 30% will prevent the sandmixture from filling the hard-to-get-at points of the patterns becausewithin the remaining mixture delivery time will be insufficient fordelivering the required amount of sand mixture into the molding chamber.

It is also recommended to deliver compressed air in meeting currents.

Said method of compressed air delivery is practicable when usinglarge-size molding chambers.

This object is also achieved by providing an apparatus for realizationof the method for the production of single-use foundry molds comprisingplates arranged in pairs and constituting a molding chamber; the twoside plates, arranged opposite each other being installed immovablywhile the two other counteropposed plates are installed movably with aprovision for reciprocating motion, each plate having a cavity andchannels for the passage of air through said cavity while one of theremaining plates has a slot for the delivery of said mixture into themolding chamber which incorporates a pattern plate rigidly mounted onone of the movable plates and has air channels arranged coaxially withthe channels of said plate, a source of compressed air and a means forits periodical communication with the molding chamber wherein, accordingto the invention, the apparatus has an air discharge system periodicallycommunicated with the molding chamber, and at least one additional platerigidly secured on the outside to the fixed side plate and provided atthe side of the latter with a hollow which, together with said fixedplate, forms an air chamber, the additional plate having a means for thedelivery of compressed air into the air chamber, said meanscommunicating with the compressed air source and said fixed side platehas channels for the delivery of compressed are through the air chamberinto the molding chamber.

It is practicable that the molding chamber should incorporate anadditional pattern plate rigidly installed on another movable plate andhaving channels arranged coaxially with the channels of said movableplate.

Such a structural arrangement of the apparatus for the realization ofthe method for the production of single-use foundry molds provides forthe realization of the method permitting the air to be discharged fromthe molding chamber due to a provision in the apparatus of an airdischarge system which ensures uniform compaction of sand mixture in thevolume of the mold.

Besides, the provision in the apparatus of at least one additional platehaving a means for delivery of compressed air into the air chamberwherefrom is, flows into the molding chamber ensures the air deliveryinto the molding chamber in the direction parallel to the pattern platewhich improves the filling of narrow deep hollows in the patterns withsand mixture and its preliminary compaction.

The provision in the molding chamber of an additional pattern plateensures the possibility of making high-quality two-sided foundry moldsof a complex configuration.

Thus, the above-stipulated conditions for the method for the productionof single-use molds and the design of the apparatus for realizationthereof ensure uniform compaction with sand mixture of narrow deepspaces in the mould which improves the quality of the molds of a complexconfiguration and the possibility of making single-use two-sided foundrymolds.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention given below are its concreteexamples with reference to the appended drawings, in which:

FIG. 1 is a schematic diagram of the apparatus for realization of themethod for the production of single-use foundry molds, according to theinvention, front view, longitudinal section;

FIG. 2--section II in FIG. 1;

FIG. 3 is a schematic diagram of the foundry mold produced by theclaimed method in the apparatus illustrated in FIGS. 1, 2, front view;and

FIG. 4 is the same mold as shown in FIG. 3, with partial cutawaysection, left-hand view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The method for the production of foundry molds is realized as follows.

0.1-1 s before the delivery of sand mixture into the molding chamberprovided with a pattern plate, the air is discharged from said chamberin order to create intensive horizontal air streams therein. The air isdischarged in the direction perpendicular to the pattern plate. Then,the sand mixture is delivered by the air stream into the molding chamberin the direction parallel to the pattern plate and, upon expiration of aperiod of time equal to about 8-60% of the duration of sand mixturedelivery, said mixture is preliminarily compacted by compressed air. Thecompressed air is delivered into the molding chamber in the directionparallel to the pattern plate within the period of time equal to about5-30% of the duration of mixture delivery, i.e. the delivery ofcompressed air is completed before the end of sand mixture delivery.

The air continues to be discharged from the molding chamber in thecourse of mixture delivery and said discharge ends concurrently with theend of mixture delivery. Then, the sand mixture is compacted bypressing.

The apparatus for the realization of the method for the production ofsingle-use foundry molds comprises pairwise arranged plates 1, 2 (FIG.1), 3, 4 (FIG. 2), 5, 6 (FIG. 1) which form the molding chamber 7, asource of compressed air 8, a means for putting said source in periodiccommunication with the molding chamber 7, and a system 10 for thedischarge of air from the molding chamber 7. Two side plates 3, 4 (FIG.2) arranged opposite each other are immovable.

The apparatus is provided with at least one additional plate and thenumber of such plates is selected in accordance with the overalldimensions of the molding chamber 7 and may reach four. In this case,said additional plates may be installed on plates 1, 2 (FIG. 1), 3, 4(FIG. 2), respectively.

In the embodiment of the invention considered here the apparatus isprovided with two additional plates 11, 12 secured rigidly from outsideto the fixed side plates 3, 4 with bolts 13. Each additional plate 11,12 has a hollow at the side of the corresponding plate 3, 4, said hollowand said plate forming an air chamber 14, 15. The plates 3, 4 havechannels 16, 17 for the delivery of compressed air through thecorresponding air chambers 14, 15 into the molding chamber 7.

Two counteropposed plates 5, 6 (FIG. 1) are installed movably with aprovision for reciprocating motion and each of them is connected withthe rod 18 of the hydraulic cylinder (not shown in the Drawings).

Each movable plate 5, 6 is provided with respective cavities 19, 20 andrespective channels 21, 22 for the passage of air through the respectivecavity 19, 20. The plate 2 installed movably opposite the plate 1 has aslot 23 for the delivery of mixture into the molding chamber 7, saidmixture entering the slot 23 from the sand-blasting tank (not shown inthe Drawing).

Arranged inside the molding chamber 7 are two pattern plates 24, 25fastined rigidly by bolts 26 on the movable plates 5, 6. Each patternplate 24, 25 has respective air channels 27, 28 arranged coaxially withchannels 21, 22. Secured with bolts 29 to the pattern plates 24, 25(FIG. 2) are patterns 30, 31, respectively. Each pattern 30, 31 has arespective channel 32, 33 arranged coaxially to the correspondingchannels 27, 28 of the corresponding pattern plate 24, 25.

The means 9 (FIG. 1) for putting the compressed air source 8periodically in communication with the molding chamber 7 is made in theform of a cock 34 and pipelines 35, 36 communicating with the cavities19, 20. Connected to the cock 34 is a system 10 for the discharge of airfrom the molding chamber 7 constituting by a vacuum pump 37communicating with a vacuum tank 38. The discharge system 10 is putperiodically in communication with the cock through the pipeline 39. Thecock 34 is capable of communicating periodically with the compressed airsource 8 with the air discharge system 10. Each additional plate 11, 12(FIG. 2) is provided with a means 40 for delivering compressed air intoa respective air chamber 14, 15. The means 40 is, essentially, acompressed air tank 41 communicating with a valve 42 and, through apipeline 43, with the respective air chambers 14, 15.

The apparatus for the realization of the method for the production ofsingle-use foundry molds, according to the invention, functions asfollows.

The cavities 19, 20 are put in communication by the cock 34 (FIG. 1)through pipelines 35, 36 with the air discharge system 10 creating apressure differential between the cavities 19, 20 and the mouldingchamber 7 so that the air is discharged from the molding chamber 7through channels 27, 28 and 21, 22 in the direction perpendicular to thepattern plates 24, 25. The discharge of air in the directionperpendicular to the pattern plates 24, 25 is required for creatingsteady air streams in the molding chamber 7 directed towards the patternplates 24, 25, perpenducularly thereto. Inasmuch as the air is aninertia medium, the creation of steady air streams of the requireddirection takes a certain period of time so that the discharge of airhas to begin before the start of sand mixture delivery into the moldingchamber 7. In the considered example, the discharge of air from themolding chamber is started 0.5 s before the beginning of mixturedelivery. Generally speaking, this time period may range from 0.1 to 1 sbecause the time period shorter than 0.1 s is insufficient for creatingthe steady air streams perpenducular to the pattern plates while thedischarge of air started more than 1 s before the delivery of sandmixture is uneconomical since the stream have already been reliablyformed so that the energy of the discharge of air is expended fornothing. Besides, this increases the total time of the mold productioncycle thus reducing the efficiency of the apparatus.

After the air streams directed towards and perpendicularly to thepattern plates 24, 25 have been reliably formed, the sand mixture isdelivered after said time interval (0.5 s) through the slot 23 by theair stream into the molding chamber 7 in the direction parallel to thepattern plates 24, 25. The particles of sand mixture moving in the airstream parallel to the pattern plates 24, 25 are carried by the airstreams directed towards and perpenducularly to the pattern plates 24,25, filling the narrow deep hollows of the patterns 30, 31. In order tosecure this movement of mixture particles within the entire process offilling the molding chamber 7, the air has to be discharged in theabove-specified direction up to the completion of delivery of sandmixture into the molding chamber 7.

After a period of time equal to about 8-60% of the time of delivery ofthe sand mixture, said mixture is preliminarily compacted by compressedair. In the embodiment discussed herein this period of time is taken tobe 10% of the mixture delivery duration. Compressed air is suppliedthrough pipelines 43 (FIG. 2) into the air chambers 14, 15 wherefrom itflows through channels 16, 17 into the molding chamber 7 in thedirection parallel to the pattern plates 24, 25. Compressed air isdelivered under a pressure somewhat higher than the pressure of air usedfor the delivery of sand mixture, the compressed air being delivered inmeeting streams through two additional plates 11, 12.

If the apparatus has one additional plate which is expedient in the caseof a small-volume molding chamber, the compressed air is delivered inone stream directed parallel to the pattern plates.

However, the compressed air stream may be delivered either from twosides (meeting streams) into small molding chambers or from one side (asingle stream) into large-size molding chambers. In the latter case, itbecomes necessary to increase the cross-sectional areas of the means 40for the delivery of compressed air and to increase the compressed airpressure.

Compressed air is delivered into the molding chamber 7 in the directionparallel to the pattern plates 24, 25 because the air streams moving inthis direction interact with the air streams directed towards thepattern plates 24, 25, perpendicularly thereto, and thus ensurecompaction of the sand mixture in the narrow deep hollows of thepatterns 30, 31 and uniform compaction of the mixture throughout thevolume of the foundry mold, except the zones near the plates whosechannels 16, 17 admit compressed air into the chamber 7.

In case of any other direction of compressed air stream, there appearair streams in the chamber 7, directed against the air streams whichcarry the sand mixture towards the pattern plates 24, 25 and,consequently, interfere with filling the narrow deep hollows or patterns30, 31 with sand mixture, thus imparing the quality of foundry molds.

Compaction of the sand mixture reduces its volume and the jets of theair delivered into the molding chamber 7 interfere with filling thecompressed air delivery zones with sand mixture so that there appearvoids and looseness near the plates 3, 4 whose channels 16, 17 deliverthe compressed air; said voids can be filled only by stopping thedelivery of compressed air before the end of mixture delivery into themolding chamber 7. Within the time between the end of air delivery andthe end of mixture delivery the sand mixture entering the moldingchamber 7 will freely fill these voids and will be compacted there,ensuring uniform distribution of density throughout the volume of thefoundry mold. Thus, the compressed air must be delivered into themolding chamber within the time period equal to 5-30% of the duration ofmixture delivery into the molding chamber 7, i.e. the duration of airdelivery should be smaller than the time of mixture delivery. When thetime of air delivery is 5% less than the mixture delivery time, theeffect of action of air is insufficient while in case of air deliverytime longer than 30% it will be not enough for the mixture to fill thevoids because within the remaining time of its delivery the moldingchamber 7 will not receive the required amount of mixture.

In the described example, the compressed air is delivered into thechamber 7 within the period equal to 20% of the duration of mixturedelivery in the direction parallel to the pattern plates 24, 25.

As soon as the molding chamber 7 has been filled with the sand mixture,its delivery through the slot 23 (FIG. 1) is discontinued simultaneouslystopping the discharge of air from the molding chamber 7. For thispurpose the cavities 19, 20 are disconnected from the air dischargesystem 10 by means of the cock 34. The plates 5 and 6 are moved towardseach pther, compacting the sand mixture finally by pressing. Then, thecock 34 puts the cavities 19, 20 in communication with the compressedair source 8 and simultaneously the plates 5 and 6 are moved away fromeach other, extracting the patterns 30, 31 from the mold. Compressed airdelivered through channels 21, 22, 27, 28 creates the air streamsdirected perpendicularly to the pattern plates 24, 25 towards the moldand ensuring easy extraction of patterns 30, 31 from the mold withoutbreakage of their high and thin parts.

EXAMPLE 1

0.1 s before the beginning of mixture delivery, the air is dischargedfrom the molding chamber in the direction perpendicular to the patternplates and continues to be discharged also during the delivery of sandmixture.

The sand mixture consisting of, wt %:

    ______________________________________                                        bentonite     10                                                              amylomite     0.2                                                             quartz sand   the balance                                                     ______________________________________                                    

is delivered by the stream of air under a pressure of 0.3 MPa into amolding chamber having two pattern plates in the direction parallel tosaid plates. Sand mixture characteristics: compression strength 0.15MPa, rupture strength 0.016 MPa, moisture content 3-3.5%.

Duration of mixture delivery is 1 s. Then, the mixture is preliminarilycompacted by the compressed air delivered in the direction parallel tothe pattern plates. This compressed air is delivered by the meetingstreams 0.5 s after the mixture delivery (which amounts to 50% of theduration of mixture delivery) and in the course of 0.2 s (20% of theduration of mixture delivery).

Then, the sand mixture is compacted by pressing at a force of 10kgf/cm².

Now, the compressed air is delivered through the pattern plates,concurrently withdrawing them from the mold and extracting the patterns.

The results of twenty two similar experiments conducted under similarconditions are summarized in Table 1.

A criterion for assessing the standard of compaction is the hardnessparameter, determined with a hardness meter. The surface hardness of themold is determined in points 1 through 11 shown in the mold diagram inFIGS. 3 and 4.

The results of tests are given in Table 2.

The disclosed method for the production of foundry molds and theapparatus for realization thereof ensure the high-quality impression ofthe patterns on both sides of the foundry mold, high efficiency ofproduction by mating two-sided molds of a complex configuration in asingle molding chamber and a considerable broadening of nomenclature ofcastings produced by flaskless horizontal stack molding in automaticproduction lines.

INDUSTRIAL APPLICABILITY

Most successfully this invention can be utilized in automatic flasklessmolding lines in the production of castings of complex configuration.

                  TABLE 1                                                         ______________________________________                                                          Preliminary compaction of                                                     sand mixture                                                                   Air               duration                                       Chamber      discharge                                                                              time before                                                                            of                                       Ex-   overall      from     delivery of                                                                            mixture                                  ample dimensions,  chamber, sand mixture                                                                           delivery                                 No.   mm           s        %    s     %   s                                  1     2            3        4    5     6   7                                  ______________________________________                                         1    250 × 250 × 250                                                                 0.05    30   0.12  20  0.8                                 2    250 × 250 × 250                                                                0.1      30   0.12  20  0.8                                 3    250 × 250 × 250                                                                0.5      30   0.12  20  0.8                                 4    250 × 250 × 250                                                                1.0      30   0.12  20  0.8                                 5    250 × 250 × 250                                                                1.5      30   0.12  20  0.8                                 6    250 × 250 × 250                                                                0.5       7    0.028                                                                              20  0.8                                 7    250 × 250 × 250                                                                0.5       8    0.032                                                                              20  0.8                                 8    250 × 250 × 250                                                                0.5      40   0.16  20  0.8                                 9    250 × 250 × 250                                                                0.5      60   0.24  20  0.8                                10    250 × 250 ×  250                                                               0.5      65   0.26  20  0.8                                11    250 × 250 × 250                                                                0.5      40   0.32   4  0.016                              12    250 × 250 × 250                                                                0.5      40   0.32   5  0.02                               13    250 × 250 × 250                                                                0.5      40   0.32  20  0.08                               14    250 × 250 × 250                                                                0.5      40   0.32  30  0.12                               15    250 × 250 × 250                                                                0.5      40   0.32  35  0.14                               16    250 × 250 × 250                                                                0.5      40   0.32  20  0.08                               17    250 × 250 × 250                                                                0.5      40   0.32  20  0.08                               18    250 × 250 × 250                                                                0.5      40   0.32  20  0.08                               19    250 × 250 × 250                                                                0.5      40   0.32  20  0.08                               20    250 × 250 × 250                                                                0.5      40   0.32  20  0.08                               21    250 × 250 × 250                                                                0.5      40   0.32  20  0.08                               22    900 × 700 × 700                                                                0.5      40   0.32  20  0.08                               ______________________________________                                        Ex-   Duration of                                                                              Pressing                                                     ample mixture    force,     Relation of depth to                              No.   delivery, s                                                                              kgf/cm.sup.2                                                                             width of pattern hollow                           1     8          9          10                                                ______________________________________                                         1    0.4        10         2.0                                                2    0.4        10         2.0                                                3    0.4        10         2.0                                                4    0.4        10         2.0                                                5    0.4        10         2.0                                                6    0.4        10         2.0                                                7    0.4        10         2.0                                                8    0.4        10         2.0                                                9    0.4        10         2.0                                               10    0.4        10         2.0                                               11    0.4        10         2.0                                               12    0.4        10         2.0                                               13    0.4        10         2.0                                               14    0.4        10         2.0                                               15    0.4        10         2.0                                               16    0.4        10         0.1                                               17    0.4        10         0.3                                               18    0.4        10         1.0                                               19    0.4        10         3.0                                               20    0.4        10         3.5                                               21    0.4        10         2.0                                               22    0.4        10         2.0                                               ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Surface hardness in points, units                                             1     2     3     4   5   6   7   8   9   10  11  Remarks                     ______________________________________                                         1. 85    40    80  85  80  82  82  80  40  85  85                                                    Loosely-                                                                                  compacted                                                                     thin                                                                          protruding                                                                    parts of mold                                                      2. 85 83 85 85 83 85 87 85 83 88 88 Molds of                                             good quality                                                       3. 85 85 85 85 85 85 85 85 85 85 85 Same                                      4. 87 86 87 85 85 86 85 86 85 87 88 Same                                      5. 87 86 85 86 85 85 85 86 86 87 88 Impracticable                            5                                                                                         conditions                                                         6. 88 70 75 80 70 75 83 75 70 80 88 Molds of                                             nonuniform                                                                    density                                                            7. 85 85 85 85 83 85 87 85 83 88 88 Molds of                                             good quality                                                       8. 85 85 85 85 84 85 85 85 84 85 85 Same                                      9. 85 85 85 85 85 84 85 84 85 85 85 Same                                     10. 85 75 80 85 50  0 70 75 50 70 80 Voids and                                            looseness                                                         11. 85 85 85 85 65  0 75 85 85 85 85 Same                                     12. 85 85 85 85 85 85 85 85 85 85 85 Molds of                                             good quality                                                      13. 86 85 86 86 87 85 86 85 85 85 85 Same                                     14. 86 86 85 85 86 80 86 85 85 86 86 Same                                     15. 86 86 86 86 70  0 76 85 86 85 86 Voids and                                            looseness                                                         16. 86 85 86 86 85 85 86 85 86 86 86 Molds of                                             good quality                                                      17. 86 85 86 85 85 85 86 85 86 86 86 Same                                     18. 86 80 86 85 85 85 86 85 80 86 86 Same                                     19. 86 78 86 85 85 85 86 85 78 86 86 Same                                     20. 86 40 86 85 85 85 86 85 40 86 86 Loosely-                                             compacted                                                                     thin                                                                          protruding                                                                    parts of mold                                                     21. 86 86 86 85 85 85 86 85 86 86 86 Molds of                                             good quality                                                      22. 85 87 86 85 86 86 87 85 86 86 86 Same             ______________________________________                                    

We claim:
 1. A method for producing single-use foundry molds comprisingthe steps of:pneumatically delivering a sand mixture into a moldingchamber having at least one pattern plate, in a direction of movement ofsaid sand mixture parallel to said at least one pattern plate;delivering at least one unidirectional stream of compressed air directlyinto said molding chamber in order to thereby produce a preliminarycompaction of said sand mixture, said step of delivering said at leastone unidirectional stream of compressed air being initiated with a timedelay relative to the initiation of said step of pneumaticallydelivering said sand mixture; finally compacting said sand mixture bymechanical pressing; characterized in that said step of delivering saidat least one unidirectional stream of compressed air directly into saidmolding chamber to thereby produce a preliminary compaction of said sandmixture is performed within a predetermined period of time; said step ofdelivering compressed air causes a retardment and interruption of saidstep of pneumatically delivering said sand mixture; and said step ofpneumatically delivering said sand mixture is completed after thetermination of said step of delivering compressed air.
 2. A method asclaimed in claim 1, wherein said step of delivering compressed air intosaid molding chamber in order to thereby produce a preliminarycompaction of said sand mixture is continued for a time period equal to5-30 percent of the duration of said step of pneumatically deliveringsaid sand mixture.
 3. A method as claimed in claim 1, wherein saidcompressed air is delivered into said molding chamber in a directionparallel to said pattern plate.
 4. A method as claimed in claim 1,wherein said compressed air is delivered into said molding chamber in adirection parallel to said pattern plate and perpendicular to saiddirection of movement of said sand mixture.
 5. A method as claimed inclaim 1, wherein said compressed air is delivered into said moldingchamber in two meeting streams.
 6. A method as claimed in claim 1,further comprising the step of discharging air from said moldingchamber, said step of discharging air preceding said step ofpneumatically delivering said sand mixture into said molding chamber andbeing terminated concurrently with the end of said step of sand mixturedelivery.
 7. An apparatus for producing single-use foundry moldscomprising:a molding chamber (7), said molding chamber having a bottomplate (1), a top plate (2), a first and a second oppositely disposedimmovable side plates (3, 4), a first and a second oppositely disposedreciprocatingly movable side plates (5, 6), a slot (23) for delivering asand mixture into said molding chamber, said slot being provided in saidtop plate, a cavity (19, 20) and channels (21, 22) for the passage ofair, said cavity and said channels being located in each one of saidfirst and second movable side plates, at least one pattern plate (24)rigidly installed on one of said movable side plates, and air ducts (28)located in said at least one pattern plate coaxially with said channels(22) for the passage of air; a source (8) of compressed air; means (9)for putting said source of compressed air periodically intocommunication with the molding chamber; and an air discharge system (10)periodically put into communication with said molding chamber (7);characterized in that said molding chamber includes: at least oneadditional plate (11) rigidly secured to an outer side of said firstimmovable plate (3), said at least one additional plate having a hollowforming with the first immovable side plate an air chamber (14), and airpassages (16) located in said first immovable side plate, said airpassages communicating said air chamber with said molding chamber; andwherein said apparatus further comprises means (4) communicating saidair chamber with said compressed air source (8).